msvfw32: Exclude unused header

[Andrew Talbot]

Changelog:
    msvcrt20: Exclude unused header.

diff -urN a/dlls/msvfw32/mciwnd.c b/dlls/msvfw32/mciwnd.c
--- a/dlls/msvfw32/mciwnd.c	2007-01-18 12:47:12.000000000 +0000
+++ b/dlls/msvfw32/mciwnd.c	2007-05-11 20:13:28.000000000 +0100
@@ -28,7 +28,6 @@
 #include "winnls.h"
 #include "wingdi.h"
 #include "winuser.h"
-#include "winreg.h"
 #include "winternl.h"
 #include "vfw.h"
 #include "digitalv.h"